The invention has to do with a magnetic valve, in particular a self-controlling magnetic valve, which is actuated by an electromagnetically controlled initial pilot valve for controlling fluids. The valve has a main valve member in the form of a differential piston and the means to suppress pressure surges when the main valve closes. It includes an overflow channel that has a limited flow-through cross section between both sides of the main valve member, and whose cross section increasingly lessens in the final phase of the closing motion.
It has been noticed that cavitation occurs when magnetic valves are closed abruptly, such as in magnetic valves that are used to control water flow in devices like dishwashers and washing machines, particularly those with servocontrol valve functions. This causes noises similar to hammer blows. Additionally, on the inlet side, an impact-like increase in pressure is noted. Efforts have been made to protect against these types of pressure surges by using elastic hoses as inlet and outlet lines. Recently, however, for safety reasons, the magnetic valves in question have been installed directly on the water faucet, and/or linked to the feeding system via lines that are as short as possible and relatively inelastic. For this reason, a proposal has already been made (European Patent No. 0,135,474) to create pressure equalization volumes operating by spring tension, on both the inlet and outlet sides. But such efforts to find a solution are expensive and costly. In addition, with own-medium-controlled magnetic valves, efforts have been made to lessen pressure surges on the inlet and outlet flow sides by giving the overflow channel of the servo valve mechanism a very small cross section, making it possible for the main valve to perform only a delayed closing. However, with this there is a danger that sedimentation and/or dirt particles carried by the controlled fluid will obstruct the channel, and the valve then will no longer be able to close.
Additionally, the German Patent Specification No. 976 465 describes an own-medium-controlled magnetic valve according to the generic name. It has an overflow channel that runs vertically through the main valve member, and its cross section is increasingly reduced during motion achieved by having a housing-stable conical pin project into the overflow channel. However, only a quite gradual cross section reduction of an overflow channel, which is relatively narrow even without this, can be achieved, so that the valve closes only after a time lag. Additionally, there is the danger that lime deposits will make the cross section relationships uncontrollable, and/or lead to abrasion of the overflow channel walls.
The French Patent Specification No. 1,514,837 offers a self-controlling magnetic valve, also generic, with a rubber elastic membrane that comes into contact on the one hand with the main valve seat, and on the other may be supported radially outside the main valve seat by a ring-shaped fold vis-a-vis the overpressure that acts on it from in the inlet side, under control of a ring-shaped member on a stiff plate surface of the main valve member. The ring-shaped member has, bilaterally, a collar of fine radial grooves, through which a pressure equalization is accomplished between the two sides of the main valve member. Although the flow-through cross section of the flow path so created, may be reduced toward the end of the closing motion with increasing contact pressure on the membrane, it cannot go toward zero, so that the closing still ends in with a relatively impact-type motion.
Additionally, the U.S. Pat. No. 2,870,986 offers a magnetic valve that in principle is similar, in which, with increasingly overpressure from the inflow side of the valve, an overflow channel in the main valve member is increasingly restricted in a way that is largely independent of the particular setting of the main valve member, so that the membrane is compressed into an annular groove of a plate-shaped support member. With the "reinforcement member" so created, the valve's flow rate should be stabilized in relation to the pressure that appears.
Here again, as in the other case, a danger exists that the flow-through cross section of the flow path in question can be reduced in the course of time by deposits.